Implant retaining device

ABSTRACT

There is provided an implant retaining device, which has the effect of preventing an intervertebral implant from jutting out of the receiving bed. The implant retaining device generally includes a plate having at least one throughbore to receive a screw, and a screw for securing the plate to the vertebrae. The plate may be dimensioned to cover a portion of the opening of a receiving bed, and thus, need only be secured to a single vertebral body. In an alternate embodiment, the plate may be used during bone fracture correction procedures to prevent a bone screw from backing out of engagement with adjacent bone sections. A method of retaining an intervertebral implant using the device is also provided.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional ApplicationSerial No. 60/242,051 filed Oct. 20, 2000, the contents of which arehereby incorporated by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Technical Field

[0003] The present disclosure is directed to an implant retaining devicefor preventing an implant from backing out of a receiving bed or graftsite formed in body tissue. More specifically, the present disclosure isdirected to an implant retaining device particularly suited forretaining an intervertebral implant in a receiving bed formed betweenadjacent vertebrae.

[0004] 2. Background of Related Art

[0005] The spine is a flexible column formed of a series of bone calledvertebrae. The vertebrae are hollow and piled one upon the other,forming a strong hollow column for support of the cranium and trunk. Thehollow core of the spine houses and protects the nerves of the spinalcord. The vertebrae are connected together by means of articularprocesses and intervertebral, fibro-cartilages.

[0006] The intervertebral fibro-cartilages are also known asintervertebral disks and are made of a fibrous ring filled with pulpymaterial. The disks function as spinal shock absorbers and alsocooperate with synovial joints to facilitate movement and maintainflexibility of the spine. When one or more disks degenerate throughtrauma, spondylolisthesis or other pathologies, nerves passing near theaffected area may be compressed and are consequently irritated. Theresult may be chronic and/or debilitating back pain. Various methods andapparatus, both surgical and non-surgical, have been designed to relievesuch back pain.

[0007] One method designed to relieve such back pain is interbody spinalfusion. Typically, interbody spinal fusion involves distractingadjoining vertebrae of the spine so that the nerve root canal sizes areincreased and nerve irritation is eliminated or reduced. In order tomaintain the adjoining vertebrae in a distracted state, at least oneintervertebral implant is inserted into a receiving bed formed in thedisk space between the adjoining vertebrae. The implant is positioned toengage the adjoining vertebrae to maintain the vertebrae at a fixeddegree of distraction.

[0008] Preferably, the implant should become fused to adjoiningvertebrae in order to prevent the implant and adjoining vertebrae frommoving. The implant must also provide spinal load support between thevertebrae. Further, during the time it takes for fusion, i.e.,biological fixation of the vertebrae, to be completed, the implantshould have enough structural integrity to maintain the disk spacewithout substantial degradation or deformation of the implant.

[0009] To facilitate rapid bone growth, the implant may include or beprovided with a bone growth material. The material from which theimplant is constructed should be a biocompatible material and,preferably, interact biologically with the body's own naturallyoccurring tissues.

[0010] In order to have successful spinal fusion and maintain thestability of the spine, the vertebral implant must be fixedly positionedin relation to the adjoining vertebrae during the entire period requiredfor fusion to occur. However, the everyday activity of a patient who hasundergone a spinal fusion procedure may lead to progressive mechanicalloosening and eventual failure of the implant. This significantlydecreases the chances of obtaining successful fusion of the implant andthe adjoining vertebrae. Therefore, it is imperative that the implant befixedly retained in the intervertebral space during the period requiredfor spinal fusion.

[0011] A variety of different devices have been developed to retain anintervertebral implant at a fixed position within the intervertebralspace. These devices include, inter alia, screws and formations formedon the implant itself. Such devices often inhibit insertion of theimplant into the intervertebral space.

[0012] Accordingly, a need exists for an improved implant retainingdevice which is configured to reduce the likelihood of expulsion orretropulsion of an intervertebral implant from between adjoiningvertebrae during normal patient activity, without inhibiting insertionof the implant into the intervertebral space.

SUMMARY

[0013] In accordance with the present disclosure, an implant retainingdevice is provided which prevents expulsion of an intervertebral implantfrom an intervertebral receiving bed. In one embodiment the implantretaining device includes a plate having at least one throughboredimensioned to receive a screw. Single or multiple screws can be used tosecure the plate to the vertebrae. The plate may have a rectangular,circular, or any other configuration capable of performing the intendedfunction of preventing expulsion of an intervertebral implant from thereceiving bed.

[0014] The plate can be secured to one or both vertebral bodies toprevent the intervertebral implant from backing out of the receivingbed. The plate may be dimensioned to cover a portion of the opening of areceiving bed, and thus, need only be secured to a single vertebralbody. Alternately, the plate may be dimensioned to extend entirelyacross the disc space and may be secured to one or both of the vertebralbodies.

[0015] When the plate is formed from bone, it may be partially or fullydemineralized. Partially demineralized bone provides a degree offlexibility to the plate such that it can be manipulated to conform tothe surface to which it is secured, e.g., the vertebrae.Demineralization also improves the osteoconductive and osteoconductivecharacteristics of the plate.

[0016] In an alternate embodiment, the plate may be used in surgicalprocedures other than spinal interbody fusion procedures. For example,the plate may be used during bone fracture correction procedures toprevent a bone screw from backing out of engagement with adjacent bonesections.

[0017] Also disclosed herein is a method of retaining an intervertebralimplant in a receiving bed using the disclosed implant retaining device.The method includes attaching a plate, dimensioned to cover at least aportion of the receiving bed, to a vertebral body and securing the upperportion of the plate to the vertebral body utilizing at least one screw.Alternately, the method includes attaching a plate to adjacent vertebralbodies using at least two screws.

BRIEF DESCRIPTION OF TIE DRAWINGS

[0018] Various preferred embodiments of the presently disclosed implantretaining device are described herein with reference to the drawingswherein:

[0019]FIG. 1A is a perspective view of one preferred embodiment of thepresently disclosed implant retaining device having a rectangularconfiguration;

[0020]FIG. 1B is a perspective view of another preferred embodiment ofthe presently disclosed implant retaining device having a rectangularconfiguration aid a curvature along its transverse axis;

[0021]FIG. 1C is a top view of another preferred embodiment of thepresently disclosed implant retaining device having a circularconfiguration;

[0022]FIG. 1D is a perspective view of another preferred embodiment ofthe presently disclosed implant retaining device having a rod shapedconfiguration;

[0023]FIG. 2 is a front view of the implant retaining device shown inFIG. 1A secured to a vertebral body with a pair of screws;

[0024]FIG. 3 is a side view of the implant retaining device shown inFIG. 1A secured to a vertebral body with a bone screw to retain aconcave implant between adjacent vertebral bodies;

[0025]FIG. 4 is a side view of the implant retaining device shown FIG.1A secured to a vertebral body with a bone screw to retain a cylindricaldowel between adjacent vertebral bodies;

[0026]FIG. 5 is a side view of the implant retaining device shown inFIG. 1A utilized in a bone fracture correction procedure to prevent abone screw from backing out of engagement with adjacent bone sections;and

[0027]FIG. 6 is a cross-sectional view of another embodiment of thepresently disclosed implant retaining device having a stepped boreconfigured to receive the head of a bone screw.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0028] Preferred embodiments of the presently disclosed implantretaining device will now be described in detail with reference to thedrawings in which like reference numerals designate identical orcorresponding elements in each of the several views.

[0029] The implant retaining device of the present invention is intendedto be attached to at least one vertebral body, to cover at least aportion of the disk space to prevent a vertebral implant from backingout of a receiving bed. The implant retaining device is especiallysuited for procedures where it would be desirable to prevent an implantfrom backing out of the spine. However, it is entirely suitable toapplications involving the repair of other bony sites in the body.

[0030] In humans, the device may be used predominately in the lumbar andthoracic regions of the spine, but, is adaptable for use in the cervicalspine and other regions of the body as well.

[0031] The implant retaining device described herein may be formed ofany biocompatible material or combination of materials. “Biocompatible”means that no serious systemic toxicity is caused by the presence of thematerial in a living system. It is contemplated that biocompatiblematerials may cause some clinically acceptable amounts of toxicityincluding irritation and/or other adverse reactions in certainindividuals. For example, the material described in U.S. Pat. No.5,899,939, the contents of which are incorporated herein by reference,may be entirely suitable for fabricating all or a portion of the implantretaining device described herein.

[0032] The implant retaining device may also be fabricated from any ofthe various biocompatible polymers. Examples of biocompatible polymerssuitable for use herein would include bioabsorbable polymeric materialssuch as, for example, polymers and/or copolymers containing any of thefollowing polymerizable monomers: epsilon-caprolactone, glycolide,trimethylene carbonates, tetramethylene carbonates, dimethyltrimethylene carbonates; dioxanones; dioxepanones; absorbable cyclicamides; absorbable cyclic ether-esters derived from crown ethers;hydroxyacids capable of esterification, including both alphahydroxyacids (such as glycolic acid and lactic acid) and betahydroxyacids (such as beta hydroxybutyric acid and gamma hydroxyvalericacid); polyalkyl ethers (such as polyethylene glycol and polypropyleneglycol and combinations thereof), etc. Of course non-bioabsorbablepolymers that are biocompatible such as, for example,polytetrafluoroethylene, would also be suitable for fabricating any orall of the components of the implant retaining device described herein.

[0033] The implant retaining device may also be fabricated from metallicmaterials commonly used in the fabrication of implantable devices, forexample, surgical stainless steel, titanium, titanium alloys, etc.Ceramic materials such as, hydroxyapatite, bioglass, etc., may also beused for the fabrication of the device described herein. Of course, anycombination of materials may be used to fabricate the entire implantretaining device described herein as well as the various components ofthe fixation system herein. Any and all such combinations ofbiocompatible materials are envisioned as being within the scope of thedisclosure herein.

[0034] Referring to FIGS. 1A-D, implant retaining device 10 includes aplate 12 having at least one throughbore 14 dimensioned to receive ascrew 16 (see FIGS. 2-4). Plate 12 may vary in thickness depending onthe size and shape of the vertebral body and the vertebral implant withwhich the plate 12 is being utilized. The thickness of plate 12 may alsovary depending on whether the implant retaining device is adapted foruse in the lumbar, thoracic or cervical spinal regions, or other regionsof the body. The thickness of plate 12 may vary from at least about 0.5mm to about 1.0 cm. Preferably, plate 12 is between about 2 mm to about5 mm. Plate 12 can be formed from any biocompatible material having therequisite strength requirements including, as discussed above,cancellous or cortical bone, ceramics, polymers, composites, etc.Preferably, plate 12 is constructed from cortical bone. Plate 12 mayhave a rectangular configuration (FIG. 1A), a circular configuration(FIG. 1C), a rod shaped configuration (FIG. 1D), or any otherconfiguration capable of performing the intended function describedherein. Plate 12 may also be provided with a curvature along itslongitudinal and/or transverse axis (FIG. 1B). The curvature may beselected to correspond to the curvature of a surface against which plate12 is to be secured, e.g., a vertebrae.

[0035] Referring to FIGS. 2-4, plate 12 is suitable for use inpreventing an intervertebral implant 20 from backing out of a receivingbed 22 formed between adjacent vertebral bodies 24 and 26 during aspinal interbody fusion procedure. Intervertebral implants includecylindrical dowels (FIG. 4), wedge-shaped implants, rectangular spacers,concave or convex implants (FIG. 3), etc. During an intervertebralimplantation procedure, the intervertebral implant 20 is placed betweenadjacent vertebral bodies to support the vertebral bodies at a desiredorientation and spacing to facilitate spinal fusion. Such procedures arewell known in the art and will not be discussed in further detailherein.

[0036] After intervertebral implant 20 has been placed between vertebralbodies 24 and 26, plate 12 can be secured to one or both of thevertebral bodies 24 and 26 to prevent implant 20 from backing out ofreceiving bed 22. As illustrated, plate 12 need only be dimensioned tocover a portion of the opening of receiving bed 22, and thus, need onlybe secured to a single vertebral body. To minimize damage to thevertebral bodies, attachment to a single vertebral body is preferred.Alternately, plate 12 may be dimensioned to extend entirely across thedisc space and may be secured to one or both of the vertebral bodies(not shown).

[0037] When plate 12 is formed from bone, it may be partially or fullydemineralized using, for example, a controlled acid treatment. Plate 12may be partially demineralized to provide a degree of flexibility to theplate such that it can be manipulated to conform to the surface to whichit is secured, e.g., the vertebrae. Alternately, plate 12 may bepartially demineralized to increase the osteoinductive characteristicsof the plate. For example, the surface of the plate to be securedadjacent to a vertebral surface may be surface demineralized to promoteosteogenic growth.

[0038] In an alternate embodiment, plate 12 may be used in surgicalprocedures other than spinal interbody fusion procedures. For example,plate 12 may be used to prevent a bone screw 30 from backing out ofengagement with adjacent bone sections during bone fracture correctionprocedures. See FIG. 5. In such a procedure, after the bone screw hasbeen screwed into the bone sections 40 and 42, plate 12 can be affixedover the head 44 of the bone screw 30 to prevent the bone screw 30 frombacking out of the insertion bore. As illustrated, a single screw 16 canbe used to secure plate 12 to the bone section 42. Alternately, multiplescrews can be used to secure plate 12 to bone section 42, or bonesections 40 and 42, e.g., one screw at each end of plate 12.

[0039] The screw 16 and/or bone screw 30 can be formed from anybiocompatible material having the requisite strength requirementsincluding surgical grade metals, cancerous or cortical is bone, bonecomposites, polymers, BMP's, etc. Preferably, screws 16 and 30 areformed from cortical bone such as disclosed in U.S. application Ser. No.09/542,556, the entirety of which is hereby incorporated by reference.

[0040] A method of using the implant retaining device is also describedherein. In use, plate 12 is attached to one or more vertebral bodies 24and 26 to prevent an intervertebral implant from backing out of anintervertebral receiving bed. The plate is dimensioned to cover at leasta portion of the opening to the receiving bed and may extend over theentire receiving bed opening. Thereafter, the plate may be secured toone or both of the vertebral bodies using a bone screw or screws.Alternately, other fastening techniques may be used to secure the plateto the vertebral body or bodies, e.g., nails, adhesives, pins, etc.

[0041] It will be understood that various modifications may be made tothe embodiments disclosed herein. For example, the plate 12 may beconstructed having a variety of configurations other than thoseillustrated herein including rectangular, triangular, etc. Moreover,multiple plates may be used simultaneously, i.e., one plate may extendfrom each side of the graft site. Further, the plate may include astepped bore 15 formed about throughbore 14 to receive the head 17 ofthe screw 16. See FIG. 6. Therefore, the above description should not beconstrued as limiting, but merely as exemplifications of preferredembodiments. Those skilled in the art will envision other modificationswithin the scope and spirit of the claims appended hereto.

What is claimed is:
 1. An implant retaining device comprising: a bodydimensioned to cover at least a portion of an opening to a receiving bedformed between adjoining vertebral bodies, the body having a singlethroughbore dimensioned to receive a screw; and a screw for securingsaid body to one of the adjoining vertebral bodies.
 2. The implantretaining device as recited in claim 1, wherein said body has arectangular configuration.
 3. The implant retaining device as recited inclaim 1, wherein said body has a circular configuration.
 4. The implantretaining device as recited in claim 1, wherein said body is curvedalong its longitudinal axis.
 5. The implant retaining device as recitedin claim 1, wherein said body is curved along its transverse axis. 6.The implant retaining device as recited in claim 1, wherein said body isin the form of a plate.
 7. The implant retaining device as recited inclaim 1, wherein said body is formed from partially demineralized bone.8. A method of retaining an intervertebral implant within a receivingbed formed between adjoining vertebral bodies, the method comprising thefollowing steps: providing a retaining plate having at least onethroughbore for receiving a bone screw, the retaining plate beingdimensioned to extend at least partly across a disk space definedbetween the adjoining vertebral bodies, and attaching the retainingplate to only one of the adjoining vertebral bodies such that theretaining plate extends at least partly across the disk space betweenthe vertebral bodies.
 9. The method as recited in claim 8, wherein saidplate has a rectangular configuration.
 10. The method as recited inclaim 8, wherein said plate has a circular configuration.
 11. The methodas recited in claim 8, wherein said plate is curved along itslongitudinal axis.
 12. The method as recited in claim 8, wherein saidplate is curved along its transverse axis.
 13. The method as recited inclaim 8, wherein said plate is formed from bone.
 14. The method asrecited in claim 13, wherein the bone is cortical bone.
 15. The methodas recited in claim 13, wherein the bone is partially demineralizedbone.